Responses of Soybeans and Soybean Cyst Nematodes to Cropping Sequences

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Abstract
Nine cropping treatments were compared in fields infested with soybean cyst nematodes (SCN) in Arkansas, Missouri, and Tennessee for 6 yr. Seven continuous-culture treatments were six race 3-resistant soybean lines with varying levels of resistance to race 4 (including resistant Bedford and susceptible Forrest) and a 70:30 Bedford/Forrest blend. Two rotations, Bedford with nonhost crop and Bedford with Forrest and SCN-susceptible Essex, were included. At the three locations, there was a trend for more SCN reproduction on race 4-resistant cultivars relative to susceptible cultivars after the resistant cultivars were grown for 4-6 yr. However, cyst densities did not significantly increase, and seed yields of continuously grown resistant cultivars were not significantly different from those of resistant cultivars in alternative cropping treatments. At the Arkansas and Missouri locations, seed yields of the susceptible and resistant cultivars were not significantly different. In Tennessee, mean seed yield for 6 yr of continuous Bedford was 515 kg/ha greater than for continuous Forrest. Cyst densities in soil of continuous Forrest plots were about 2.5 times those in continuous Bedford plots. At all locations, no treatment was superior to continuous Bedford in seed yield.